title: The impact of hydrofluoric acid etching followed by unfilled resin on the biaxial strength of a glass-ceramic.
abstract: OBJECTIVE
  To evaluate the null hypotheses that hydrofluoric (HF) acid etching time would neither decrease the biaxial flexural strength of a glass-based veneering ceramic nor enhance it after silane and unfilled resin (UR) applications.
  
  
  METHODS
  Disc-shaped IPS e.max ZirPress specimens were allocated into 12 groups: G1-control (no-etching), G2-30 s, G3-60 s, G4-90 s, G5-120 s, G6-60 s+60 s. Groups (G7-G12) were treated in the same fashion as G1-G6, but followed by silane and UR applications. Surface morphology and roughness (Ra and Rq) of the ceramics were assessed by means of scanning electron microscopy (SEM) and profilometry, respectively. Flexural strength was determined by biaxial testing. Data were analyzed by two-way ANOVA and the Sidak test (α=0.05). Weibull statistics were estimated and finite element analysis (FEA) was carried out to verify the stress concentration end areas of fracture.
  
  
  RESULTS
  The interaction (etching time vs. surface treatment) was significant for Ra (p=0.008) and Rq (0.0075). Resin-treated groups presented significantly lower Ra and Rq than non-treated groups, except for the 60s group (p<0.005). SEM revealed that etching affected the ceramic microstructure and that the UR was able to penetrate into the irregularities. A significant effect of etching time (p=0.029) on flexural strength was seen. G7-G12 presented higher strength than G1-G6 (p<0.0001). None of experimental groups failed to show 95% confidence intervals of σ0 and m overlapped. FEA showed lower stress concentration after resin treatment.
  
  
  CONCLUSIONS
  HF acid etching time did not show a damaging effect on the ceramic flexural strength. Moreover, the flexural strength could be enhanced after UR treatment.
authors.affiliation: Indiana University School of Dentistry, Department of Restorative Dentistry/Division of Dental Biomaterials, Indianapolis, IN 46202, USA.
authors.forename: Sumana
authors.initials: S
authors.lastname: Posritong
authors.forename: Alexandre Luiz Souto
authors.initials: AL
authors.lastname: Borges
authors.forename: Tien-Min Gabriel
authors.initials: TM
authors.lastname: Chu
authors.forename: George J
authors.initials: GJ
authors.lastname: Eckert
authors.forename: Marco A
authors.initials: MA
authors.lastname: Bottino
authors.forename: Marco C
authors.initials: MC
authors.lastname: Bottino
mesh_terms: D002516:Ceramics; D020342:Finite Element Analysis; D005898:Glass; D006858:Hydrofluoric Acid / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D012117:Resins, Synthetic; D013499:Surface Properties
chemical_list: D012117:Resins, Synthetic; D006858:Hydrofluoric Acid
keywords: Biaxial strength; Glass ceramic; Hydrofluoric acid; Unfilled resin; Veneers